Interconnecting processing units of a stored program controlled system using free space optics

ABSTRACT

Internal communication signals in a stored program controlled system comprising a plurality of units configured to process signals are provided by a free space optical beam line which is proximal to all of the plurality of units. The free space beam line is configured to contain optically encoded signals which comprises signals transmitted between and/or among the plurality of units. Each unit includes a probe for injecting optically encoded signals in the free space beam line and/or and for receiving optically encoded signals from the free space beam line. Advantageously, there may be a first terminal at a first end of the beam line to configure to transmit and terminate the optically encoded signals and a second terminal unit at the second end of the free space beam line configured to transmit and terminate the optically encoded signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to U.S. patent application AttorneyDocket No. C. C. Byers 41-3, entitled “Interconnecting Processing UnitsOf A Stored Program Controlled System Using Time Division MultiplexedFree Space Optics”, filed concurrently herewith and commonly assigned toLucent Technologies Inc., and incorporated by reference herein, withpriority claimed for all commonly disclosed subject matter.

[0002] This application is also related to U.S. patent applicationAttorney Docket No. C. C. Byers 42-4, entitled “InterconnectingProcessing Units Of A Stored Program Controlled System Using WavelengthDivision Multiplexed Free Space Optics”, filed concurrently herewith andcommonly assigned to Lucent Technologies Inc., and incorporated byreference herein, with priority claimed for all commonly disclosedsubject matter.

[0003] This application is also related to U.S. patent applicationAttorney Docket No. C. C. Byers 43-5, entitled “InterconnectingProcessing Units Of A Stored Program Controlled System Using SpaceDivision Multiplexed Free Space Optics”, filed concurrently herewith andcommonly assigned to Lucent Technologies Inc., and incorporated byreference herein, with priority claimed for all commonly disclosedsubject matter.

[0004] This application is also related to U.S. patent applicationAttorney Docket No. C. C. Byers 44-6, entitled “Installation OfProcessing Units Into A Stored Program Controlled System Wherein TheComponent Processing Units Are Interconnected Via Free Space Optics”,filed concurrently herewith and commonly assigned to Lucent TechnologiesInc., and incorporated by reference herein, with priority claimed forall commonly disclosed subject matter.

FIELD OF THE INVENTION

[0005] This invention relates to the field of stored program controlledsystems, including, but not limited to, telephone switching offices,data routers, and robotic machine tools; and, more specifically, thisinvention describes an optical communication path providingcommunication among processing units in a stored program controlledsystem.

BACKGROUND OF THE INVENTION

[0006] The background of the present invention may be summarized in oneword: “wires”. Most stored program controlled systems of even minorcomplexity consist of a plurality of single or limited functionalityprocessing units, each of which is connected to one or more of the otherprocessing units by wires. There are literally millions of miles ofinterconnecting wires in current use in systems as diverse as storedprogram controlled telephone and data switching systems, roboticassembly lines, high speed mainframe computers, modem aircraft, localarea networks, etc.

[0007] These wires provide the medium for communication signals amongprocessing units to facilitate functionality of the whole. For example,a signal generated by a processing unit in the cockpit of an airplane istransmitted over a wire to a processing unit in the tail section tomanipulate the tail control surfaces. Likewise, in a stored programcontrolled telephone switching office, a signal to connect a telephonecall from one line to another is carried by wires interconnecting theprocessing units to which the telephone lines are connected.

[0008] In most stored program control systems, the “interconnectingwires” is a complex array of backplane wiring interconnecting processingunits on cards, shelves of cards and cabinets of shelves. Each of these(card, shelf of cards, cabinet of shelves) may be considered a“processing unit”, because cards and shelves of related tasks areusually wired together in functional units, and then generally wiredtogether in a cabinet. Cabinets of large stored program controlledsystems are interconnected by bundles of wires (cables). Thus, theinterconnecting wires provide communications paths that enable theindividual processing units of the stored program controlled system tointeract, thus providing the functioning of the whole.

[0009] A single change in an individual processing unit of a storedprogram controlled system may cause literally thousands ofinterconnecting wires to be moved from one processing unit to another,or connected or reconnected in some fashion. These new connections mustbe carefully planned and executed by skilled craftspeople who make eachconnection and then test it. One minor error may cause a majormalfunction.

[0010] Further, these wires are bulky and are frequently groupedtogether into a cable bundle. Such bundling is problematic in and ofitself; in that, if one or more wires in the bundle is cut, then some orall of the functionality of the stored program controlled system islost, and it is difficult to find one damaged wire in a bundle of wires.In a worst case scenario, a single short in a bundle of wires can causedevastating fires, such as the fire in the telephone switching office inHinsdale, Ill. in May of 1988. This fire caused a nationwide disruptionof telephone service that lasted for a few days and interruption oflocal telephone service that lasted for several months.

[0011] Over the past decade, some interconnecting wire has been replacedby fiber optical cable. This was an advance in the art, because moresignals (higher bandwidth) are carried over a smaller physicalcross-section. However, fiber optics has been treated for the most partlike another wire: each fiber connects one processing unit to another,the optical signal is converted between optical and electrical signalsat each terminus, and the electrical signals are processed in the usualfashion.

[0012] Therefore, a problem in the art is that processing units in astored program controlled processing system are interconnected byextensive wiring which is difficult to install, maintain and modify.

SUMMARY OF THE INVENTION

[0013] This problem is solved and a technical advance is achieved in theart by a system and method that uses free space optics to interconnectprocessing units of a stored program controlled system. Communicationsignal paths are provided in a stored program controlled systemcomprising a plurality of units configured to process signals(“processing units”) by a beam line in free space, proximal to each ofthe plurality of units. The beam line is configured to contain opticallyencoded communications signals that are transmitted between and amongthe processing units. Each processing unit includes a probe forreceiving optically encoded signals from the beam line, and,advantageously, a probe for injecting optically encoded signals into thebeam line. There may be a first terminal unit at a first end of the beamline configured to originate and/or terminate the optically encodedsignals and a second terminal unit at the second end of the beam linealso configured to originate and/or terminate the optically encodedsignals.

[0014] Each processing unit may comprise a frame, a shelf, or anindividual card on a shelf of the stored program controlled system, andeach processing unit performs functions related to the stored programcontrolled system's intended functionality. Probes are configured toreceive or send optically encoded signals in the free space beam line.The probe further comprises supporting circuitry to translate opticallyencoded signals into and out of electrically encoded signals, and routesuch signals.

[0015] The beam line may run above, below, through or adjacent to theprocessing units and the beam may be encoded in time divisionmultiplexing, spatial division multiplexing or wavelength divisionmultiplexing. The beam line may be formed and directed using routingmirrors, prisms, lenses, gratings and holograms.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A more complete understanding of this invention may be obtainedfrom a consideration of the specification taken in conjunction with thedrawings, in which:

[0017]FIG. 1 is a perspective view of a free space beam lineillustrating the relationship of the beam line and probes according to ageneral overview of an exemplary embodiment of this invention;

[0018]FIG. 2 is a cross-sectional view of the free space beam line takenalong line 2-Z of FIG. 1;

[0019]FIG. 3 is an exemplary embodiment of transmitting and receivingprobes of FIGS. 1 and 2;

[0020]FIG. 4 is another exemplary embodiment of transmitting andreceiving probes of FIGS. 1 and 2;

[0021]FIG. 5 is a block diagram of uni-directional communication along afree space beam line according to one exemplary embodiment of thisinvention;

[0022]FIG. 6 is a block diagram of a further exemplary embodiment ofthis invention having bi-directional probes;

[0023]FIG. 7 is a block diagram of another exemplary embodiment of thisinvention wherein each of the processing units may communicate with eachother;

[0024]FIG. 8 is a physical layout of a stored program controlledswitching office according to an exemplary embodiment of this invention;

[0025]FIG. 9 is a block diagram of the exemplary embodiment of FIG. 8 inwhich the free space beam line is distributed to each shelf; and

[0026]FIG. 10 is a block diagram of the exemplary embodiment of FIG. 8in which the free space beam line is distributed to each card on eachshelf.

DETAILED DESCRIPTION

[0027] Turning to FIG. 1, a perspective view of a free space beam line10 according to one exemplary embodiment of this invention is shown.According to this exemplary embodiment, a free space beam line 10 isgenerated by a transmitter 12 within a transmitting probe 14 whichprojects optically encoded signals, as will be described below inconnection with FIGS. 3 and 4. Transmitting probe 14 produces a beamline 10 of desired diameter along the length of its path.

[0028] A plurality of receivers 16 within receiving probes 18 aredistributed throughout beam line 10 along the outer periphery in theform of a spiral or helix, in this exemplary embodiment. Other possibleconfigurations of probes along the beam line will be apparent to oneskilled in the art after studying this disclosure. Receiving probes 18are distributed in a helix in this exemplary embodiment so that there isa minimal amount of shadowing; that is, one receiving probe 18 being inthe shadow of a previous receiving probe 18 in beam line 10 causing theprobe in the shadow to receive little or none of the optically encodedsignals in beam line 10.

[0029] Free space beam line 10 may be contained within a reserved volumeor conduit 22, in an enclosure, such as a cylinder or pipe or,alternatively, may be in the open. If the beam line 10 is contained in aconduit, then the interior surface may be coated at the time ofmanufacture to be optically absorptive or optically reflective dependingupon the length of the pipe, the wavelength of the signal generated bythe laser within transmitter 12 and loss budget to provide optimalreception of optically encoded signal by the plurality of receivingprobes 18 throughout the length of beam line 10.

[0030] Conduit 22 includes, in this exemplary embodiment, a firstterminal unit 24 and a second terminal unit 26. First terminal unit 24includes a transmitting probe 14 and second terminal unit 26 includes areceiving probe 18, in this exemplary embodiment. First terminal unit 24originates optical beam line 12 and second terminal unit 26 terminatesthe portion of optical beam line 12 passing beyond the other probes 18.As will be discussed further, below, first terminal unit 24 and/orsecond terminal unit 26 may include both transmitters and receivers, andmay be interconnected to recycle the encoded signal.

[0031]FIG. 2 illustrates a view looking down a cross-section of freespace beam line 10 taken along line 2-2 of FIG. 1. Conduit 22 includes aplurality of receiving probes 18 around its inner edge. In theillustration of FIG. 2, the laser of transmitter 12 (FIG. 1) focusesbeam line 10 to encompass the interior circumference of conduit 22whereby each probe 18 receives the encoded optical signal. Secondterminal unit 26 is illustrated herein as comprising a receiving probe18. (Second terminal unit may also include a transmitter 12, not shown.)Alternatively, second terminal unit 26 may comprise an end cap. An endcap may be absorptive in order to stop the beam line 10 or may bereflective (i.e., a mirror or retroreflector) to recycle beam line 10 inthe opposite direction.

[0032] Turning now to FIG. 3, exemplary embodiments of a transmittingprobe 14 and a receiving probe 18 are shown. In this exemplaryembodiment, transmitting probe 14 includes a transmitter 12 comprising alaser 30 (i.e., a laser diode 32 and a feedback photodetector 34, asknown in the art), which converts electronically encoded signals intofree space optical beam line 10. Free space optical beam line 10 isprojected through a concave lense 36 and a convex lense 38 (which form areverse Galilean telescope, as is known in the art). A laser driver 40feeds electrically encoded signals to, and receives feedback from, laser30, as known in the art. Feedback amplifier 42 regulates the input tolaser 30. Laser 30 and laser driver 40 are both known to those skilledin the art. Laser 30 and laser driver 40 are illustrated herein as twoseparate units, but may be one unit.

[0033] Free space beam line 10 is received at a receiving probe 18 at areceiver 16, which includes a convex lense 44 that focuses beam line 10on a photodetector 46. Photodetector 46 receives a portion of beam line10 and generates an electrical signal in response thereto. Theelectrical signal is fed into a receiver circuit 48 comprising atrans-impedance amplifier (TIA) 50, clock recovery circuit 52 anddecision circuit 54. Receiver 16 and receiver circuit 48 are well knownin the art. Receiver 16 and receiver circuit 48 are illustrated hereinas two separate units, with receiver circuit 48 contained within asignal receiver 55. However, these two units may be one unit, as isknown in the art.

[0034] Laser 30 is driven by an electrical signal from signal generator56. Signal generator 56 comprises laser driver 40, protocol handler 58and multiplexer 60. Multiplexer receives multiple inputs 62 from one ormore processing units, which are multiplexed according to apredetermined algorithm (many algorithms for multiplexing are known inthe art and are thus not discussed here). Signals are then passed toprotocol handler 58. Protocol handler 58 encapsulates the signals withthe protocol used by the beam line 10. Such protocols are described inU.S. patent applications Attorney Docket Nos. Byers 41-3, Byers 42-4 andByers 43-5 which are incorporated by reference, above. The signalgenerated by protocol handler 58 is fed into laser driver 40, whichcontrols laser 30.

[0035] When a signal is received by photodetector 46, it is delivered tosignal receiver 55, which comprises receiver circuit 48, protocolhandler 64 and demultiplexer/router 66. The received signal is decodedin receiver circuit 48, as known in the art. The receiver circuit 48 isconnected to a protocol handler 64 which de-encapsulates the signalreceived according to the protocol used by protocol handler 58. Protocolhandler 64 passes the signal to a demultiplexer and router 66 whichdemultiplexes the signal and then sends signals 68 to the receivingprocessing unit or units. Demultiplexing and routing algorithms are wellknown in the art, and are thus not futher described.

[0036]FIG. 4 illustrates an exemplary embodiment of a transmitting probe14 and a receiving probe 18 according to another aspect of thisinvention. In this exemplary embodiment, the electronics are remote fromthe optical beam line. Transmitting probe 14 in this exemplaryembodiment includes a transmitter 12 comprising a laser element 30, asdescribed above in connection with FIG. 3, which changes electricalsignals delivered from laser driver 40 into an optically encoded signal.Optionally, this optically encoded signal is fed into lense 80, whichprojects the signal through light guide 82 (i.e., optical fiber) in thisexemplary embodiment. One skilled in the art will appreciate that someapplications will not require lense 80. Fiber optic conduit 82 projectsthe optically encoded signal through lenses 36 and 38 (the reverseGalilean telescope as described above) which forms free space beam line10.

[0037] Receiving probe 18 includes a receiver 16, a lense 306 thatfocuses light from beam line 10 onto fiber optic conduit 86. Fiber opticconduit 86 transmits the optical signal through lense 88 ontophotodetector 46. Photodetector 46 sends an electrical signal throughreceiver circuit 48, protocol handler 64 and demultiplexer/router 66, asdescribed above. The signals are delivered to their respectiveprocessing unit or units via lines 68.

[0038]FIG. 5 is a block diagram of a stored program controlled system100 in a basic implementation of an exemplary embodiment of thisinvention. Stored program controlled system 100 may comprise, in thisexemplary embodiment, a unidirectional local area network. In the storedprogram controlled system 100, a first processing unit 102 comprises acontroller which distributes signals to a plurality of processing units104, 106, 108 and 110. Processing units 104, 106, 108 and 110 receivesignals from controller 102 via receiving probes 18 (as described above)and perform their respective functions on received signals.

[0039] In this one-way communication system, processing unit(controller) 102 passes commands to processing units 104, 106, 108 and110 without expecting responses from any of the processing units.Controller 102 generates signals to control processing units 104, 106,108 and 110 and encodes the signals into a form that can be translatedinto optical signals (as discussed above in connection with FIG's. 3 and4). Controller 102 is connected to a transmitting probe 14 in a firstterminal unit 24 in this exemplary embodiment.

[0040] A free space beam line 10 is thus formed containing the opticallyencoded signals for processing units 104, 106, 108 and 110. Theexemplary embodiment of FIG. 5 includes a conduit 22. Conduit 22includes an end cap 112 (instead of a second terminal unit) which may becoated with light absorptive or alternatively reflective material,depending upon which direction the receiving probes 18 are facing.

[0041] According to this invention, the entirety of free space beam line10 is filled with optically encoded signals as it exits terminal unit24. In this embodiment, each probe receives the optically encoded signaldirectly. Alternatively, lenses 36 and 38 in transmitter 12 (FIG. 3) oftransmitting probe 14 may focus the beam line 10 so that it does notcompletely fill conduit 22 until it hits end cap 112. End cap 112comprises reflective surface in this exemplary embodiment, whichprovides a full beam line 10 throughout conduit 22. Considerations ofsignal strength, beam divergence, bit rate, distance between processingunits 104, 106, 108 and 110, signal to noise ratio, etc. must be takeninto account to determine which method (direct or reflective) oftransmission is preferable in a given application.

[0042] Turning now to FIG. 6, an exemplary embodiment of this inventionusing bi-directional probes is shown generally at 120. In this exemplaryembodiment, processing unit (controller) 122 communicates with aplurality of processing units 124, 126, 128, and 130. As in the previousexemplary embodiments, controller 122 communicates with a first terminalunit 24, which includes a transmitting probe 14 that produces free spacebeam line 10. Beam line 10 is, in this exemplary embodiment, unenclosed.

[0043] Each processing unit 124, 126, 128 and 130 has an associatedreceiving probe 18 for receiving signals from controller 122.Additionally, each processing unit 124, 126, 128 and 130 includes atransmitting probe 14 to transmit return signals to receiving probe 16in terminal unit 24. The received signals are delivered to controller122, which then processes these signals for further control of thestored program controlled unit, creating a full-duplex channel.

[0044] Turning now to FIG. 7, a further exemplary embodiment of thisinvention is shown. In this exemplary embodiment, free space beam line10 is unidirectional, i.e., signals flow in the direction fromuni-directional first terminal unit 132 to second unidirectionalterminal unit 134 and are then recirculated, as will be describedfurther below. Free space beam line 10 is enclosed in conduit 22. Inthis exemplary embodiment, a processing unit controller 136 andprocessing unit 138, 140, 142 and 144 are each connected to a respectivetransmitting probe 14. Processing units 138, 140, 142 and 144 areconnected to respective receiving probes 18. Terminal 134 uses terminalreceiving proble 135.

[0045] In the exemplary embodiment of FIG. 7, processing unit orcontroller 136 originates electrical control signals for processingunits 138, 140, 142 and 144 and communicates such signals to router 146.Router 146 comprises a conventional router as is known in the art.Router 146 communicates signals for processing units 138, 140, 142 and144 to a signal generator 56 (as described above in connection with FIG.3). Transmitter 14 in unidirectional first terminal unit 132 opticallyencodes the signals, and transmits optical beam line 10. Receivingprobes 18 receive the optically encoded signals and convey them to theirrespective processing unit 138, 140, 142 and 144. Each processing unit138, 140, 142 and 144 may send feedback or other information tocontroller 136 by injecting signals into free space beam line 10, whichare all received at terminal receiving probe 135 in unidirectionalsecond terminal unit 134. The signals are then fed back to router 146where they may be farther circulated in beam line 10 or delivered tocontroller 136.

[0046] Systems using many of the embodiments of this invention (i.e.,FIG. 7) must include features to prevent messages from recirculating infree space beam line 10. If these features are not included, infinitefeedback loops are possible, where a single message is continuouslyrelayed between two endpoints and/or probes, quickly absorbing allavailable bandwidth. To prevent this, a means to break these loops isprovided. Router 146 is programmed (or programmed in conjunction withthe probes or endpoints) to detect addresses that lead to looping andnot forward those messages back into the beam line. Alternately, theoptical characteristics of the beam line, transmitters and receivers arecontrolled to prevent messages from a given source from circulatingindefinitely.

[0047]FIG. 8 presents a block diagram of one exemplary embodiment of astored program controlled system which uses a free space optical beamline 10 to interconnect its processing units. In this exemplaryembodiment, the stored program controlled system comprises a telephoneswitching system 200, such as a 5ESS® Switch or 7R/E Switch manufacturedby Lucent Technologies. There are a plurality of processing units 202,204, 206, 208, 210 and 212. Processing units 202, 204, 206, 208, 210 and212 comprise “frames” as are known in the art. Each frame comprises aplurality of shelves 214 and on each shelf is one or more cards 216(also called “boards” in the art). Each card 216 performs one or morepredefined functions, as is known in the art.

[0048] In the exemplary embodiment of a 5ESS® Switch, frame 202comprises a communications module (CM) which effects communication amongthe other frames in the system. Frame 204 comprises an administrationmodule (AM) which provides overall control of the system andhuman-machine interface. Frames 206, 208, 210 and 212 comprise switchmodules (SMs), which support a plurality of line and/or trunk units (orsome combination thereof) and effect connections of telephone or datacalls. All of the processing units (frames 202, 204, 206, 208, 210 and212) communicate with each other (generally through CM 202) in order toswitch telephone calls.

[0049] Currently, frames such as 202, 204, 206, 208, 210 and 212 areinterconnected by a plurality of wire buses and/or optical fiber carriedin overhead trays or under raised floors. Wiring a new office or evenadding a new frame may cause the installation team to revisit the entirewiring of the system in order to ensure proper functionality of thewhole stored program controlled system 200 when connected. Thisinvention is intended to replace the current industry standard of wiringbetween and among frames in central switching offices. This inventioneliminates the probability of accidental damage to cabling, decreasesnew installation and upgrade time. The following exemplary embodiment ofthis invention is described in the context of such a central switchingoffice. It is, however, clear to one skilled in the art how to implementand use this invention in other applications after a review of thispatent application.

[0050] According to one exemplary embodiment of this invention, a freespace optical beam line 10 provides interconnection of the frames 202,204, 206, 208, 210 and 212. Signals are carried on one or more opticalwavelengths as is known in the art. There may also be a pilot beam 218in the visible light wavelengths in order to aid craft personnel toalign probes 14 & 18 of the processing units and other opticalcomponents.

[0051] In this exemplary embodiment, each processing unit 202, 204, 206,208, 210 and 212 includes a transmitting probe 14 and a receiving probe18 positioned in beam line 10 in order to send and receive,respectively, signals in system 200. Each transmitting probe 14 and eachreceiving probe 18 may, advantageously, be bi-directional. It is withinthe scope of one skilled in the art to make the transmitting andreceiving probes of FIG's. 3 and 4 transmit/receive in both directionsafter reading this specification. Transmitting probe 14 and receivingprobe 18 on frame 202 comprise a first terminal unit 24 and transmittingprobe 14 and receiving probe 18 on frame 208 comprise a second terminalunit 26. The probes 14 and 18 in first terminal unit 24 and secondterminal unit 26 may be uni-directional.

[0052] Each transmitting probe 14 is connected to a signal generator 56and each receiving probe 18 is connected to a signal receiver 55. Signalgenerator 56 and signal receiver 55 may be separate cards 216 asillustrated, may be one integrated card, or may both be integrated withother functionality of its respective shelf 214 and/or frame 202, 204,206, 208, 210 or 212.

[0053] Additionally, first terminal unit 24 may be connected to secondterminal unit 26 by way of a connector 220. Routers 222 and 224 areillustrated herein as connecting connector 220 to first terminal unit 24and second terminal unit 26, respectively. Ordinary routers 222 and 224may route selected messages between terminal units 24 and 26, and toprevent endless looping of messages. Connector 220 may comprise anotherfree space optical conduit like beam line 10, or may comprise a fiberoptic or electrical link as is known in the art.

[0054] Free space beam line 10 may be manipulated by turning mirrors226, prisms or the like (not shown but well known in the art) toprovide, for example, a continuous beam line 10 through multiple rows ofprocessing units (or floor levels, etc.). Beam line 10 is illustrated asrunning above the processing units in FIG. 1. Beam line 10 may also rununder a raised floor, or in a space or conduit otherwise adjacent to orthrough the processing units.

[0055] Turning now to FIG. 9, another exemplary embodiment of thisinvention is shown, wherein “processing units” are defined at one levelbelow a frame. In this exemplary embodiment, free space beam line 10 isshown, as described above. Each frame, for example, frame 204, comprisesa plurality of shelves 214, here shown as 214A-D. In this exemplaryembodiment, a turning mirror 226 is set in main beam line 10 to turnmain free space beam line 10 into frame-level free space beam lines 228.In this exemplary embodiment, transmitting probes 14 and receivingprobes 18 send and receive optical signals for each shelf 214A-D. Endcards 230 on each shelf 214A-D comprise signal generators 56 and signalreceivers 55 (not shown) as described above in connection with FIG. 3.Mirrors 226 may be partially reflective so as to turn a portion of thesignal beams and allow another portion to pass through, as is known inthe art.

[0056] Turning now to FIG. 10, another exemplary embodiment is shown,wherein a “processing unit” is now defined as a card 215. Turningmirrors 226 are again used to turn main free space beam line 10 intoframe free space beam lines 228. Each shelf 214A-214D includes a pair ofadditional card level turning mirrors 240 in beam lines 228,respectively. Card level turning mirrors 240 provide card free spacebeam lines 242. There may be one or more card level beam lines 242 pershelf 214. In this exemplary embodiment, there are two free space beamlines 242 per shelf. Each shelf 214 then includes at least one card 216equipped with a transmitting and/or receiving probes 14 and 18 (asillustrated in FIG. 3) and the supporting signal generator and signalreceiver.

[0057] Frame probe 249 is used for frame-level communication and controlfunctions. For example, power control, temperature sensing and alarmannunciation may be communicated to a central control by frame probe249.

[0058] It is to be understood that the above-described embodiments aremerely illustrative principles of the invention and that many variationsmay be devised by those skilled in the art without departing from thescope of this invention. It is, therefore, intended that such variationsbe included within the scope of the following claims.

What is claimed is:
 1. A system to provide internal communication in astored program controlled system comprising a plurality of processingunits, said system comprising: a free space beam line configured tocontain optically encoded signals transmitted among said plurality ofprocessing units; means in one of said plurality of processing units forinjecting optically encoded signals into said beam line; and meansconnected to each of said plurality of units for receiving opticallyencoded signals from said beam line.
 2. A system to provide internalcommunication in a stored program controlled system in accordance withclaim 1 wherein: said plurality of processing units are configured toprocess signals and each of said processing units configured to performone or more functions in response to said signals.
 3. A system toprovide internal communication in a stored program controlled system inaccordance with claim 2 further including means for translatingoptically encoded signals into electrical signals connected between eachof said means for receiving optically encoded signals and each of saidplurality of processing units.
 4. A system to provide internalcommunication in a stored program controlled system in accordance withclaim 1 wherein said means for receiving optically encoded signals aredistributed helically in said free space beam line.
 5. A system toprovide internal communication in a stored program controlled system inaccordance with claim 1 further including: a first terminal unit at afirst end of said free space beam line configured to transmit saidoptically encoded signals.
 6. A system to provide internal communicationin a stored program controlled system in accordance with claim 5 whereinsaid first terminal unit is further configured to receive opticallyencoded signals.
 7. A system to provide internal communication in astored program controlled system in accordance with claim 5 furtherincluding a second terminal unit configured to receive optically encodedsignals.
 8. A system to provide internal communication in a storedprogram controlled system in accordance with claim 7 wherein said secondterminal unit is further configured to transmit optically encodedsignals in said free space beam line.
 9. A system to provide internalcommunication in a stored program controlled system in accordance withclaim 7 wherein said second terminal unit is configured to send signalsto said first terminal unit via a means for transmitting signalsseparate from said free space beam line.
 10. A system to provideinternal communication in a stored program controlled system inaccordance with claim 9 wherein said means for transmitting comprises anoptical fiber.
 11. A system to provide internal communication in astored program controlled system in accordance with claim 9 wherein saidmeans for transmitting comprises a second free space beam line.
 12. Asystem to provide internal communication in a stored program controlledsystem in accordance with claim 9 further including a router connectedbetween said means for transmitting signals and said first terminalconfigured to route optical signals received at said second terminal topredetermined means for receiving optically encoded signals.
 13. Asystem to provide internal communication in a stored program controlledsystem in accordance with claim 1 wherein said free space beam line isunenclosed.
 14. A system to provide internal communication in a storedprogram controlled system in accordance with claim 1 wherein said freespace beam line is in a conduit.
 15. A system to provide internalcommunication in a stored program controlled system in accordance withclaim 14 wherein said conduit includes an interior surface, wherein saidinterior surface is reflective.
 16. A system to provide internalcommunication in a stored program controlled system in accordance withclaim 14 wherein said conduit includes an interior surface, wherein saidinterior surface is light absorptive.
 17. A system to provide internalcommunication in a stored program controlled system in accordance withclaim 14 wherein said conduit includes a reflective end cap.
 18. Asystem to provide internal communication in a stored program controlledsystem in accordance with claim 14 wherein said conduit includes alight-absorptive end cap.
 19. A system to provide internal communicationin a stored program controlled system in accordance with claim 1 furtherincluding means for transmitting optically encoded signals into saidfree space beam line associated with one or more means for receivingoptically encoded signals.
 20. A system to provide internalcommunication in a stored program controlled system in accordance withclaim 19 wherein said means for receiving and said means fortransmitting comprises a bi-directional probe.
 21. A system to provideinternal communication in a stored program controlled system inaccordance with claim 1 wherein each of said plurality of processingunits comprises a frame, said frame having a plurality of cards forperforming functions and wherein said frame receives optically encodedsignals from said means for receiving optically encoded signals,translates said optically encoded signals into electronically encodedsignals, and performs functions related to said plurality of cards. 22.A system to provide internal communication in a stored programcontrolled system in accordance with claim 21 wherein said frame isfurther configured to translate electronically encoded signals intooptically encoded signals after one or more of said cards performs itsrespective function, and transmits said optically encoded signals insaid free space beam line.
 23. A system to provide internalcommunication in a stored program controlled system in accordance withclaim 1 wherein said free space beam line runs above said processingunits.
 24. A system to provide internal communication in a storedprogram controlled system in accordance with claim 1 wherein said freespace beam line runs below said units.
 25. A system to provide internalcommunication in a stored program controlled system in accordance withclaim 1 wherein said means for sending and said means for receivingcomprises a probe.
 26. A system to provide internal communication in astored program controlled system in accordance with claim 25 whereineach of said probes includes an optical/electrical interface.
 27. Asystem to provide internal communication in a stored program controlledsystem in accordance with claim 25 wherein each of said units includes atransmit and receive units.
 28. A system to provide internalcommunication in a stored program controlled system in accordance withclaim 1 wherein each of said plurality of units comprises a frame, saidframe including a plurality of shelves, each of said shelves including aplurality of processing cards, and wherein said frame receives opticallyencoded signals from said free space beam line and distributes saidoptically encoded signals to each of said shelves within each frame. 29.A system to provide internal communication in a stored programcontrolled system in accordance with claim 28 further including a probeconnected to each shelf for sending and receiving optically encodedsignals and translating said signals out of and into electricallyencoded signals and distributing said signals among its plurality ofprocessing cards.
 30. A system to provide internal communication in astored program controlled system in accordance with claim 28 whereineach of said shelves distributes said optically encoded signals to eachof said processing cards.
 31. A system to provide internal communicationin a stored program controlled system in accordance with claim 28 wheresaid free space beam line is distributed to said shelves via turningmirrors.
 32. A system to provide internal communication in a storedprogram controlled system in accordance with claim 31 wherein saidturning mirrors comprise partially silvered mirrors.
 33. A system toprovide internal communication in a stored program controlled system inaccordance with claim 1 further including a pilot beam in the visiblelight spectrum.
 34. A system to provide internal communication in astored program controlled system in accordance with claim 1, including arouting function that prevents recirculation of messages that lead toinfinite looping.
 35. A system to provide internal communication in astored program controlled system in accordance with claim 1, where theoptical characteristics of the said free space beam line preventinfinite feedback loops.
 36. A method for transporting signals amongunits in a stored program controlled system, said method comprising thesteps of: optically encoding said signals; transmitting said opticallyencoded signals in a free space beam line; receiving said opticallyencoded signals at each of said processing units; and transmittingfurther optically encoded signals from each of said processing units.37. A method in accordance with claim 36 wherein the step of receivingcomprises translating said optically encoded signals into electricalsignals and said step of transmitting comprises translating electricalsignals into optically encoded signals.
 38. A method in accordance withclaim 36 wherein each unit comprises a frame having a plurality ofshelves and wherein the step of receiving comprises routing theoptically encoded signals to each shelf in said frame.
 39. A method inaccordance with claim 36 wherein the step of receiving further comprisestranslating said optically encoded signals into electrical signals ateach of said shelves and said step of transmitting comprises translatingelectrical signals into optically encoded signals at each of saidshelves.
 40. A method in accordance with claim 36 wherein each shelfincludes a plurality of processing cards and wherein said step ofreceiving comprises routing the optically encoded signals to each cardin said frame.
 41. A method in accordance with claim 40 wherein the stepof receiving further comprises translating said optically encodedsignals into electrical signals at each of said plurality of processingcards said step of transmitting comprises translating electrical signalsinto optically encoded signals at each of said processing cards.